Rheostat



March 7, 1944. s rr 2,343,425

RHEOSTAT Filed May 25, 1942 I2 INSULATION l8 I6 22 19 INVENTQR. HOWARD H. SMITH ATTORNEYS Patented Mar. 7, 1944 2,343,425 minos'rn'r Howard H. Smith, Washington, D. 0., assignor to Automatic Electric Laboratories, Inc., a, corporation of Delaware Application May 25, 1942, Serial No. 444,384

8 Claims.

The present invention relates to rheostats and has for one of its objects the provision of an improved rheostat of simple, rugged and economical construction which is positive and reliable in operation.

It is another object of the invention to provide an improved rheostat structure which is so arranged that the resistor elements thereof are substantially fully protected against damage occasioned by careless handling.

According to another object of the invention, edge wound resistor strips are used in the structure and provisions are made for securely clamping the resistance wire in place to prevent the convolutions thereof from slipping along the supporting strips.

According to still another object of the invention, provisions are made whereby the supporting structure itself is used to provide guide rails over which a wiper carrying runner may be slidably moved.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawing in which Fig. 1 is an end perspective view of an improved rheostat characterized by the features of the present invention; Fig. 2 is an end sectional view of the rheostat structure shown in Fig. 1; and Fig. 3 is a circuit diagram illustrating the manner of connecting the resistor strips and wipers forming a part of the rheostat shown in Fig. 1.

Referring now more particularly to the drawing, the rheostat there illustrated comprises a supporting structure formed of two elongated rigid metal members Ill and II. Preferably, these pieces are die stamped from flat metal stock and each thereof comprises a central web and two spaced-apart edge flanges defining a channel therebetween. Thus the member In comprises a central web Illa, a front edge flange [b, and a rear edge flange I00. The other member ll similarly comprises a central web Ila, a front edge flange Nb, and a rear edge flange Hc. At opposite ends of each of these members two integrally formed mounting lugs are provided which, if desired, may be drilled and tapped to receive assembly screws. In the assembly of the structure, the two channel-shaped members l0 and II are placed back to back so that the edge flange thereof extend in opposite directions. A pair of flat elongated resistor elements I2 and I; are disposed flatwise within the channels de fined by the edge flanges of the two supporting members l0 and l I. Each of these elements is of the edge wound resistance wire type. Thus the resistor element i2 is shown as comprising a flat strip of mica or other insulating material [4, around which are tightly wound the convolutions I5 of resistance wire which may, for example, be German silver wire. The structure further comprises a pair of elongated metal cover strips [8 and H which are disposed to overlie the outer surfaces of the resistor elements l2 and I3. In order to insulate the exposed resistance wire from the supporting members Ill and II and the cover strips I6 and I1, insulating strips [8, I9, 20 and 2| are provided which are respectively inserted between the surfaces of the resistor elements and the adjacent surfaces of the supporting members and cover strips. providing two clamping screws 22 and 23 which extend through registering openings provided in the cover strips, the insulating strips and the webs of the supporting members, and are suitably insulated from the convolutions of resistance wire by means of insulating sleeves or the like. The two terminal ends of the resistance wire convolutions, as brought out at the same end of the supporting members In and H, may be connected to terminals 24 and 25 which are suitably mounted upon one of the rear edge flanges Inc and Ho of either of the two supporting members I0 and II.

It will be noted that when the assembly is completed, a rigid structure is formed in which the edges of the resistor elements are protected against contact with other objects by the four edge flanges of the two supporting members 10 and II. It will also be noted that the outer surfaces of the resistor elements are, to a large extent, protected by the cover strips l6 and I1. These strips also serve to clamp resistance wire against the supporting strips upon which they are wound, and thus prevent longitudinal shifting of the convolutions thereof. More specifically, the only exposed surfaces of the resistor elements [2 and I3 are those which lie between the left edges of the elements as shown in Fig. 2 and the left edges of the cover strips I 6 and I1. These exposed surfaces of the resistor elements l2 and 13 are arranged to be traversed by the wipers 26 and 21, respectively, of a wiper element 28 which is carried by a substantially c-shaped runner 29. More specifically considered, the runner 29 is shaped snugly to envelop the oppositely directed front edge flanges Nb and l lb of the two supporting members 10 and H and is freely slidable The assembly is completed by therealong. This runner is of suflicient length to preclude any possibility of its binding against the flanges lb and III) as it is slid back and forth along these flanges. The wiper element 28 is substantially U-shaped in configuration and is formed of a resilient conductive material, such, for example, as brass. It is provided at its free ends with the inwardly disposed ;Wipers-- 26 and 21 which extend in opposite directions along tm longitudinal axis of the supporting members I and II and are biased to engage the resistance Wire convolutions of the two resistor elements I2 and I3. Preferably, each of the wipers 25 and-21 is slotted in the manner shown to-provide-a plurality of contact fingers each of which is more or bent away from the resistance Wire attheir-extremities' in or der to present a rounded 'suriace for contacting 1 the resistance wire. The 'possibility ofthe finger ends -bcomin'g-hookd '-un"der one or more oonvolu'tions of the resistancewire is thuspreclu'de'd. The wiper element 28 is space'd apart-and insulated from? the runner 29 b-y means of r a blockof 'i-nsulating material tfl. Assembly screws 3 I which are'suitably insulatewfrom the wiper element 28 an-d are threaded into the" runner-"29; are-- provided forniaintainingth runner and the wiper elem'enti-n assembled relationship.

An actuating-"mechanism ofithe'cor'd and pulley type is provided for slidingtheassembled'runner 29 and wiper element -28 back and forth along the front edge flanges ifib -a'n'd llb or: the two supporting members ML and I I in order :to change the setting of i the-"two 'wipers' 2 B a'rid 21 and-thus alter the-series resistance included between the te'Iminals I 24 Sand 25. -Briefiy oonsidered; this mechanism-com rises an idler pulley 32, a :drivin'g pulley 33, and an en'dless co1 d 34 which extends around I the two pulleys and =-is looped-around the u per: assembly screw- 3 l -to' be clampe'd against the surface of the wiper element 28. with a shaft- 35 which may-.be' sui'tably journaled in the structure upon which -the rhe'ostat-is mounted. 1 Similarly, the -driving -'pulley 33 :is rigidly mounted upon a sha'ft 36' WhiCh iS-fimirnale'd' in bearingsiprovide'd in the rheostat supporting structure and is provided with an extension upon which an actuating knob =31 may be mounted. 'With this-arrangement; asthe knob' 31 is manuallyrotated inthe countercloclswise direction, for example; the cord 34 is drawn around the idler pulley i 32 -by the':driving.' pulley 33 inaa direction'such that the-runner 29 and the-wiper element '28 are moved toward the upper or left end of thesuppo'rtingmembers I0 and I I, as illustrated in Fig. l of the drawing. The -reverse movement of the runner-29' and' thewiper element 23 obviouslyoccurs when-theknob- 315s rotated in the clockwise direction. Irrorder to limit the movement of the runner-"29- andthe wiperelement 28, stops 38 and 39 may be provided at either end'oi theedgefia'nge I 0b of the siippo'rting-member Ii! in the-pathofmovem'ent of the runner 29. These stops arepreferably in the form of screws, threaded into the: edge'fiange HIb at -the' correct points therealong to prevent the -wipers 2 6 and" 21 from being actuated into engagement with the mounting lugs provided at'the'two' ends of the" two supporting members.

-While .1 one embodiment of the inven'tion has been-disclosed, it will be understodd that various.

The idler-pulley 32 is carried-by and rotatable 5 modifications may be made therein which are within the true spirit and scope of the invention.

What is claimed is:

1. A rheostat comprising a supporting structure provided with a central web and a pair of oppositely directed edge flanges, a pair of resistorelements, one. of said-resistor elements being disposed on either side of said web, means securing said elements to said web, a runner slidably carried by said edge flanges and movable therealong, and wiping contacts carried by said runner and engaging said resistor elements.

A'rheostat comprising an elongated sup- ,porting'structureprovided with a central web andsaupairpf oppositely directed flanges, a pair of flat elongated resistor elements, one of said resistor elements being disposed flatwise on either side of said web, fiat cover strips overlying the outer surfaces of said resistor elements, meanssecuring said'cover" stripsiand-sai'd resistor elementsto-sai'd webso that'onlytheouter surfaces of said resistor'elements' which" arcadjacent'said flanges are "exposed; a' runn'er' slidably carried by said flanges andmovable'therealong;and'wipingcontactscarriedb'y'said runner and engaging the'exposedisurfaces'rof: said resistor elements.

3. A 'rheostat comprising Jan Jelongated supporting structure provided with'a'central Web and'a pair of oppositely directed. edgefianges, (a pair of resistor elements, one of said l resistor elements being disposedo'neither side of .said webf'means securing said .resistor 'elementsto said web,'-a"run'ner enveloping said edgeflanges and slidable therealong, and wiping -contacts carried by said runner and engagingsaid resistor elements.

4. A"rheostatcomprising an elongated ..'sup-.

porting structure providedwith a central web and a pair of oppositely-directededge flanges, a pair of-flat elongated resistorelements, one of said resistor elements beingTdi'spose'd fiatwise on either side'of said-web, flat cover stripsoverlying the outer'surfaces ofsaid resistor elements,.means securing said'cover 'strips andsaid resistorielements to said w'ebL-so .-that..-only-. the outer-.surfaces of said resistor elements which are .-.adjacent said :edge flangesare exposed-a runner enveloping. said edge fiangeswand slidable therealong, and wipingacontacts.carried by saiclrunner .an'dengagingQthe exposed surfaces-pf said resistor elements.

5. A rheostat-comprisingan elongated metallic supporting structure provided with a central web and a -pair of oppositely -directed- -flanges,--apair of.-.-fiat elongated resistor elements, oneof said resistor elements b eing disposed fiatwise on I either side of-said-web, fiat metal cover strips: overlying the outer surfaces 0f --said :resistor elements, insulating strips disposed to insulatesaid resistor elements: from-said web and: said cover strips and -meansi'securingsaid cover. strips; said resistor elements andv said insulatingystrips: to said web so thatonly the outer: surfaces of said resistor elements which are adj acent said fianges are exposed; a runner? slidablyparried byzsaid flanges and movable'therealong; and wipingrcontacts carried: by .said. runner [and :engagingzithe exposed surfaces offlsaid resistor elements.

6.' A 1 rheo'statl comprising an elongatedfsupporting structure provided with a central' web and two spaced=apartfpairs of oppositelyldirected flanges 'defin'ing -achannel on: either-'- side of said web, a resistor element disposed in each of said channels, means securing said resistor elements to said web, a runner slidably carried by one pair of said flanges and movable therealong, and wiping contacts carried by said runner and engaging said resistor elements.

7. A rlieostat comprising an elongated supporting structure provided with a central web and two spaced-apart pairs or oppositely directed flanges defining a channel on either side of said web, a fiat elongated resistor element disposed fiatwise in each of said channels, a fiat cover strip overlying the outer surface of said resistor element, means securing said cover strips and said resistor elements to said Web so that only the outer surfaces of said resistor elements which are adjacent one pair of said flanges are exposed, a runner slidably carried by said one pair of flanges and movable therealong, and wiping contacts carried by said runner and engaging the exposed surfaces of said resistor elements.

8. A rheostat comprising an elongated metallic supporting structure provided with a central web and two spaced-apart pairs of oppositely directed flanges defining a channel on either side of said web, a Hat elongated resistor element disposed flatwise in each of said channels, fiat metal cover plates overlying the outer surfaces of said resistor elements, insulating strips disposed to insulate said resistor elements from said web and said cover plates, means securing said cover strips and said resistor elements and said insuiating strips to said Web so that only the outer surfaces of said resistor elements which are adjacent one pair of said flanges are exposed, a runner slidably carried by said one pair of flanges and movable therealong, and wiping contacts carried by said runner and engaging the exposed surfaces of said resistor elements.

HOWARD H. SMITH. 

